Class MetaContentProvider

According to the:
http://docs.oasis-open.org/dita/v1.2/os/spec/archSpec/processing_key_references.html
and:
http://dita.xml.org/resource/dita-tc-faq-about-keys#Q2
if a node of a certain type makes a keyref to a topic ref on which is defined, the content of the key
will be extracted from that particular .
This content will appear inline in the Author page for that particular keyref.
It will also appear in the documentation window when the value for a keyref is computed.
The API will get called by Oxygen either when the content completion shows the user descriptions for each key reference
or when the content of a keyref is shown as static text in the editor.